1. (a) Field of the Invention
The present invention relates to an improved one-way valve structure for hydraulic jack, particularly one with a stepped inlet end at an intake hole for fixing of a filter, the diameter of the filter is slightly smaller than the inner diameter of the intake hole to make the hydraulic fluid be filtered while it is entering the pump seating so that foreign particles are completely prevented from entering the pump seating, and consequently clogging of the oil circuit or damage of the cylinder can be prevented.
2. (b) Description of the Prior Art
In the conventional hydraulic jack, such as that disclosed in the U.S. Pat. No. 4703916, an one-way valve is installed between its oil reservoir and pump seating to control hydraulic fluid flow from the oil reservoir to the pump seating, and cause the jack to lift by pushing a handle which drives a pumping cylinder and consequently a piston. The one-way valve is designed with a pressure release hole to allow the hydraulic fluid to flow to the oil reservoir through it upon overload of the jack for safety purpose and to prevent from explosion of the cylinder. However, the structure disclosed in the said patent is simply a oil circuit design without any means to prevent from invasion of foreign particles from the oil reservoir to the pump seating or pumping cylinder. Prolonged use of the jack may result in accumulation of foreign particles in the oil circuit or on the cylinder components, and even clogging of the oil circuit or damage of the cylinder. Particularly, as the inlet of the pressure release valve is relatively small, the clogging there may prevent from backflowing of the hydraulic fluid to the oil reservoir. Then, clogging at the pressure release valve which can not be discovered from its appearance may bring serious explosion and even death or injury. In other word, it is a significant negligence in design for safe operation of hydraulic jack.